How do you append to another file in python?

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Having two file names entered from users, the task is to append the content of the second file to the content of the first file.
Example 
 

Input :
file1.txt
file2.txt

Output :
Content of first file (before appending) - geeksfor
Content of second file (before appending) - geeks
Content of first file (after appending) - geeksforgeeks
Content of second file (after appending) - geeks

Algorithm : 
 

1. Enter the names of the files.
2. Open both the files in read only mode using the open() function.
3. Print the contents of the files before appending using the read() function.
4. Close both the files using the close() function.
5. Open the first file in append mode and the second file in read mode.
6. Append the contents of the second file to the first file using the write() function.
7. Reposition the cursor of the files at the beginning using the seek() function.
8. Print the contents of the appended files.
9. Close both the files.

Suppose the text files file1.txt and file2.txt contain the following data.
file1.txt 
 

file2.txt 
 

python3

firstfile = input("Enter the name of first file ")

secondfile = input("Enter the name of second file ")

f1 = open(firstfile, 'r')

f2 = open(secondfile, 'r')

print('content of first file before appending -', f1.read())

print('content of second file before appending -', f2.read())

f1.close()

f2.close()

f1 = open(firstfile, 'a+')

f2 = open(secondfile, 'r')

f1.write(f2.read())

f1.seek(0)

f2.seek(0)

print('content of first file after appending -', f1.read())

print('content of second file after appending -', f2.read())

f1.close()

f2.close()

Output : 
 

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While reading or writing to a file, access mode governs the type of operations possible in the opened file. It refers to how the file will be used once it’s opened. These modes also define the location of the File Handle in the file. The definition of these access modes is as follows:

• Append Only (‘a’): Open the file for writing.
• Append and Read (‘a+’): Open the file for reading and writing.

When the file is opened in append mode in Python, the handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data. 

Example 1: Python program to illustrate Append vs write mode.

Python3

file1 = open("myfile.txt", "w")

L = ["This is Delhi \n", "This is Paris \n", "This is London"]

file1.writelines(L)

file1.close()

file1 = open("myfile.txt", "a") 

file1.write("Today \n")

file1.close()

file1 = open("myfile.txt", "r")

print("Output of Readlines after appending")

print(file1.read())

print()

file1.close()

file1 = open("myfile.txt", "w") 

file1.write("Tomorrow \n")

file1.close()

file1 = open("myfile.txt", "r")

print("Output of Readlines after writing")

print(file1.read())

print()

file1.close()

Output:

Output of Readlines after appending
This is Delhi
This is Paris
This is LondonToday


Output of Readlines after writing
Tomorrow

Example 2:  Append data from a new line

In the above example of file handling, it can be seen that the data is not appended from the new line. This can be done by writing the newline ‘\n’ character to the file. 

Python3

file1 = open("myfile.txt", "w")

L = ["This is Delhi \n", "This is Paris \n", "This is London"]

file1.writelines(L)

file1.close()

file1 = open("myfile.txt", "a")

file1.write("\n")

file1.write("Today")

file1.write("Tomorrow")

file1 = open("myfile.txt", "r")

print("Output of Readlines after appending")

print(file1.read())

print()

file1.close()

Output:

Output of Readlines after appending
This is Delhi
This is Paris
This is London
TodayTomorrow

Note: ‘\n’ is treated as a special character of two bytes.

Example 3:  Using With statement  in Python

with statement is used in exception handling to make the code cleaner and much more readable. It simplifies the management of common resources like file streams. Unlike the above implementations, there is no need to call file.close() when using with statement. The with statement itself ensures proper acquisition and release of resources. 

Python3

L = ["This is Delhi \n", "This is Paris \n", "This is London \n"]

with open("myfile.txt", "w") as file1:

    file1.write("Hello \n")

    file1.writelines(L)

with open("myfile.txt", 'a') as file1:

    file1.write("Today")

with open("myfile.txt", "r+") as file1:

    print(file1.read())

Output:

Hello
This is Delhi
This is Paris
This is London
Today

Note: To know more about with statement click here.